This invention relates to a semiconductor device incorporating both a Hall effect element and some other active component or components that are needed in use of the device as current detector or the like. More specifically, the invention pertains to how to improve the noise immunity of such a device.
The Hall effect element or Hall generator works on the Hall effect to give an output voltage proportional to the strength of the magnetic field applied. Therefore, when placed along a current path, the Hall generator provides a voltage proportional to the magnitude of the current flowing through the path, as the current of variable magnitude creates a magnetic field of correspondingly varying strength that acts on the Hall generator.
Usually, the current detector utilizing the Hall effect is fabricated as an integrated circuit, with the Hall generator formed in a unitary semiconductor substrate in combination with a Hall voltage detector circuit and an amplifier circuit. U.S. Pat. No. 6,424,018 describes and claims an integrated Hall current detector designed for higher sensitivity. This prior art device has a current path in the form of an electrically conductive layer overlying a film of electrically insulating material on a major surface of a semiconductor substrate having a pair of Hall generators formed in juxta-position therein.
The noted prior art device has proved to have a weakness arising from the positioning of the current-path conductor layer in close proximity of the Hall generators. Not only the Hall generators but the other active components of the device were arranged so close to the current path that they were prone to give rise to errors. Such errors were easy to occur because of voltage fluctuations in the current path which manifested themselves as undesired variations in voltage between the output terminals of the Hall generators and other active circuit components.
U.S. Pat. No. 6,462,531 suggests, in a current detector using a Hall generator, a solution to the problem of how to guard the Hall generator from induction noise and external noise. The suggested solution is a noise shield in the form of a layer of electrically conductive and magnetic material, or electrically conductive and nonmagnetic material, or electrically insulating and magnetic material, overlying the Hall generator. As seen in a plan view, the noise shield is approximately the same in shape and size as the Hall generator.
This earlier solution has proved unsatisfactory, however, in shielding the required active components of the current detector other than the Hall generator. The second cited reference is totally silent on how such additional active semiconductor devices are shielded or, indeed, how they are structurally incorporated with the Hall generator at all. It is only clear that the suggested noise shield is constructionally insufficient to guard the additional active components.